The government has banned the largest sponsor of academies from taking on new schools until it dramatically improve the ones it already runs, the Guardian has learned.

The United Learning Trust (ULT) was called into the office of the schools secretary, Ed Balls, last week and told it could not sponsor any more schools until it had driven up standards in the 17 it runs and the two due to launch next September.

It follows the spectacular failure of ULT's Sheffield academies, which have been plagued with behavioural problems, have struggled to improve results and were judged inadequate by Ofsted inspectors.

The problems raise questions about government – and opposition – plans for large chains of independently run academies.

ULT is an Anglican charity chaired by the former Conservative education minster Dame Angela Rumbold, and includes the former archbishop of Canterbury Lord Carey on its board. It is the largest academy sponsor and also runs a chain of 10 private schools.

A letter signed by the schools minister, Vernon Coaker, was sent today to local authorities. It cites the two failing Sheffield academies as a reason for freezing new projects. The ULT said it "welcomed the opportunity to consolidate".

Academies are independently run, government-funded schools and, although their results have increased faster than other schools on average, there have been some high-profile failures. Four of the 200 academies have been placed in special measures.

The most recent Ofsted reports for ULT's 13 academies that have been inspected reveal that one was judged outstanding, three good, but seven were just satisfactory and two inadequate.

The letter, seen by the Guardian, says: "It is quite clear that ULT has been bold and courageous in taking on some of the most challenging predecessor schools in the country. There are very high percentages of students with free school meals and special needs at ULT academies. While there are encouraging signs, equally clearly, there is still some way to go before all ULT's academies are making consistent progress. As a result, two ULT academies are currently in Ofsted categories.

"In view of the challenges it faces, and which it acknowledges, we have asked ULT to continue to focus in particular now on its existing academies whilst developing two new potential projects."

One director of children's services for a council with a ULT academy said: "ULT has had a meeting with DSCF [the education department] and ULT was told they need to up their game. They were told they wouldn't be allowed to take on any more until they can show they have turned those schools round."

That meeting is understood to have been between the schools secretary and Sir Ewan Harper, the chief executive of the United Church Schools Trust, the charity that owns ULT.

A spokesman for ULT said its academies had steadily improved, with a 5.6 percentage point increase in the proportion of children getting five good GCSEs including English and maths – matching the national improvement for academies.

He said: "We've often taken on projects at the 11th hour or when the department has been unable to find another sponsor. So we're very happy this year to be focusing on accelerating progress at our 17 academies and working hard on the two proposed new projects for opening in 2010."

The secretary of state had expressed his enthusiasm for ULT's sponsorship of new academies in Weston Favell in Northampton and Oxford, the spokesman said.

Mary Bousted, the general secretary of the Association of Teachers and Lecturers, said: "The idea that a private provider will automatically solve deep-rooted generational problems in a school serving a poor area is simply untrue. "